Heating device for heating semiconductor wafers in thermal processing chambers

ABSTRACT

An apparatus for heat treating semiconductor wafers is disclosed. The apparatus includes a heating device which contains an assembly of light energy sources for emitting light energy onto a wafer. The light energy sources can be placed in various configurations. In accordance with the present invention, tuning devices which are used to adjust the overall irradiance distribution of the light energy sources are included in the heating device. The tuning devices can be either active sources of light energy or passive sources which reflect, refract or absorb light energy. For instance, in one embodiment, the tuning devices can comprise a lamp spaced from a focusing lens designed to focus determined amounts of light energy onto a particular location of a wafer being heated.

FIELD OF THE INVENTION

The present invention is generally directed to thermal processingchambers for heating semiconductor wafers using light energy. Moreparticularly, the present invention is directed to improved heating lampconfigurations containing tuning devices which are used to moreuniformly heat semiconductor wafers.

BACKGROUND OF THE INVENTION

A thermal processing chamber as used herein refers to a device thatrapidly heats objects, such as semiconductor wafers. Such devicestypically include a substrate holder for holding a semiconductor waferand a light source that emits light energy for heating the wafer. Duringheat treatment, the semiconductor wafers are heated under controlledconditions according to a preset temperature regime. For monitoring thetemperature of the semiconductor wafer during heat treatment, thermalprocessing chambers also typically include temperature sensing devices,such as pyrometers, that sense the radiation being emitted by thesemiconductor wafer at a selected band of wavelengths. By sensing thethermal radiation being emitted by the wafer, the temperature of thewafer can be calculated with reasonable accuracy.

In alternative embodiments, instead of or in addition to using radiationsensing devices, thermal processing chambers can also containthermocouples for monitoring the temperature of the wafers.Thermocouples measure the temperature of objects by direct contact.

Many semiconductor heating processes require a wafer to be heated tohigh temperatures so that various chemical and physical reactions cantake place as the wafer is fabricated into a device. During rapidthermal processing, which is one type of processing, semiconductorwafers are typically heated by an array of lights to temperatures, forinstance, from about 400° C. to about 1,200° C., for times which aretypically less than a few minutes. During these processes, one main goalis to heat the wafers as uniformly as possible.

Problems have been experienced in the past, however, in being able tomaintain a constant temperature throughout the wafer and in being ableto control the rate at which the wafer is heated. If the wafer is heatednonuniformly, various unwanted stresses can develop in the wafer. Notbeing able to heat the wafers uniformly also limits the ability touniformly deposit films on the wafers, to uniformly etch the wafers,beside limiting the ability to perform various other chemical andphysical processes on the wafers.

Temperature gradients can be created within the wafer due to variousfactors. For instance, due to the increased surface area to volumeratio, the edges of semiconductor wafers tend to have a cooling rate anda heating rate that are different than the center of the wafer. Theenergy absorption characteristics of wafers can also vary from locationto location. Additionally, when gases are circulated in the chamber, thegases can create cooler areas on the wafer due to convection.

In the past, various lamp configurations have been proposed in order toovercome the above described deficiencies and improve the ability toheat wafers more uniformly and to control the temperature of the wafersat various locations. These systems, however, have become increasinglycomplex and expensive to produce. For instance, some systems can containwell over 100 lamps.

As such, a need currently exists for an improved thermal processingchamber that is capable of uniformly heating semiconductor wafers in arelatively simple manner without being as complex as many prior artsystems. A need also exists for an improved rapid thermal processingchamber for heating semiconductor wafers that is equipped with controlsfor varying the amount of energy that is applied to the wafer atdifferent locations based upon the characteristics and properties of thewafer. Such controls are especially necessary due to the increasingdemands that are being placed upon the preciseness at which thesemiconductor wafers are heat treated and at which semiconductor devicesare fabricated.

SUMMARY OF THE INVENTION

The present invention recognizes and addresses the foregoingdisadvantages and others of prior art constructions and methods.

Accordingly, it is an object of the present invention to provide animproved thermal processing chamber for heat treating semiconductorwafers.

Another object of the present invention is to provide a thermalprocessing chamber having an improved lamp configuration for heating thewafers uniformly.

Still another object of the present invention to provide a heatingdevice for use in thermal processing chambers that contains a pluralityof lamps which form overlapping heating zones on a wafer being heated.

Another object of the present invention is to provide a heating devicefor use in thermal processing chambers that contains tuning devicesspaced between heating lamps for uniformly heating wafers with highlevels of controllability.

It is another object of the present invention to provide a heatingdevice for use in thermal processing chambers that not only containslamps for heating semiconductor wafers but also contains a tuning devicefor heating the wafers more uniformly, wherein the tuning devicecomprises a lamp in operative association with or without a focusinglens which is used to direct light energy being emitted by the lamp ontoa determined area of the semiconductor wafer.

Another object of the present invention is to provide a heating devicefor use in thermal processing chambers containing a plurality of lampsfor heating a semiconductor wafer and at least one passive opticalelement placed amongst the lamps which redirects light energy beingemitted by the lamps for heating semiconductor wafers more uniformly.

Still another object of the present invention is to provide a heatingdevice for use in thermal processing chambers that contains passiveoptical elements having a ruled prismatic surface which is positionedwithin the heating device in order to redirect light energy beingemitted by the heating device onto a semiconductor wafer in a mannerthat heats the wafer more uniformly.

These and other objects of the present invention are achieved byproviding an apparatus for heat treating semiconductor wafers. Theapparatus includes a thermal processing chamber adapted to contain asemiconductor wafer. For instance, a substrate holder can be containedwithin the chamber upon which the wafer is held. A heating device isplaced in communication with the thermal processing chamber which emitsthermal light energy onto the wafer held on the substrate holder. Theheating device can include an assembly of light energy sources which arepositioned, for instance, to heat different zones of the wafer. Thelight energy sources form an irradiance distribution across a surface ofthe wafer.

More particularly, during the heating process, either the semiconductorwafer can be rotated or the light energy sources can be rotated. In thismanner, the light energy sources form radial heating zones on the waferwhich aid in heating the wafer uniformly and provide good temporalcontrol during the heating cycle.

In accordance with the present invention, the heating device furtherincludes at least one tuning device positioned amongst the light energysources. The tuning device is configured to change the irradiancedistribution of the light energy sources in a manner for more uniformlyheating the semiconductor wafer. The tuning device can be an activedevice which emits light radiation onto a determined location of thewafer or can be a passive device, which redirects light radiation beingemitted by the light energy sources contained in the heating device foradjusting the irradiance distribution of the light energy sources.

In one example of an active device, the tuning device includes a lightenergy source spaced from one or more focusing lenses. The focusing lensis configured to focus light energy being emitted by the light energysource onto a determined location of the wafer. The light energy sourceand the focusing lens can be mounted to a movable support structure. Thesupport structure can be movable for directing the light energy beingemitted by the tuning device onto different locations as desireddepending upon the particular application. In general, the tuning deviceis used to supply light energy to the wafer in areas where furtherheating is desired in order to compensate for any nonuniformities in theirradiance distribution of the plurality of light energy sources.

In one embodiment, the support structure to which the light energysource is mounted includes a tiltable lever arm. The lever arm istiltable for directing light energy being emitted by the tuning deviceto a particular location.

The system of the present invention can include as many tuning devicesas are required for uniformly heating wafers. The number of tuningdevices incorporated into a particularly system will generally dependupon numerous factors, including the configuration of the light energysources. In one embodiment, the light energy sources can be placed inconcentric rings and tuning devices can be placed in between the ringsof lamps.

In order to control the amount of light energy that is emitted by theplurality of light energy sources, the apparatus of the presentinvention can include at least one temperature sensing device whichsenses the temperature of the wafer at a plurality of locations. Forinstance, the temperature sensing device can be a plurality ofpyrometers, one pyrometer with multiple viewing ports, or one or morethermocouples. The temperature sensing devices can be in communicationwith a controller, such as a microprocessor, which determines thetemperature of the wafer. The controller, in turn, can be incommunication with the power supply of the light energy sources forcontrolling the amount of heat being emitted by the light energy sourcesin response to the temperature of the wafer. The controller can beconfigured, for instance, to control the amount of light energy beingemitted by each light energy source or can control different groups ofthe light energy sources.

In one embodiment, the controller can be configured to also control theamount of light energy that is being emitted by a tuning deviceinstalled in accordance with the present invention. In particular, thecontroller can be used to control the tuning device independent of thelight energy sources. Further, the controller can also be configured tobe capable of automatically moving the support structure upon which thetuning device is mounted in order to change and adjust the location ofwhere the light energy being emitted by the tuning device contacts thewafer.

The light energy sources used in the heating device of the presentinvention can be, for instance, lamps, such as tungsten-halogen lamps.The lamps can be substantially vertically oriented with respect to thesemiconductor wafer (see FIG. 2), or can be oriented horizontally (seeFIG. 1). In order to maintain the lamps in position, the lamps can beconnected to a mounting base. The mounting base can include reflectivedevices for directing the light energy being emitted by the lamps ontothe wafer. The reflective devices can be polished annular surfacessurrounding the lamps or, alternatively, can be in the shape of platesthat extend adjacent to the lamps. For example, in one embodiment, theheating device includes reflective plates which extend beyond the lengthof the lamps in a direction perpendicular to the semiconductor wafer.

Besides using active tuning devices that emit light radiation, thepresent invention is also directed to the use of passive tuning deviceswhich redirect light energy being emitted by the light energy sources.In particular, the light energy is redirected in a manner such thatsemiconductor wafers are heated more uniformly. In this embodiment, thetuning device can comprise an optical element positioned adjacent to atleast one of the light energy sources. The optical element can bedesigned either to reflect, to absorb, or to refract light energy.

In one embodiment, the optical elements can include a ruled prismaticsurface for reflecting light radiation in a specified manner. The ruledprismatic surface can have a fixed pitch and a fixed facet angle or afixed pitch with a variable facet angle. The ruled prismatic surface canbe made from a highly reflective material, such as a dielectric materialor a metal, such as gold.

Besides having a ruled prismatic surface, in an alternative embodiment,the optical element can include a diffuse surface, which scatters lightenergy in all directions. The diffuse surface can be made from, forinstance, a rough surface.

Preferably, the passive tuning device has an adjustable position withrespect to the light energy sources contained in the heating device. Forinstance, in one embodiment, the tuning device can be placed atdifferent angles with respect to the light energy sources and at adifferent height. For instance, the light energy sources can be allattached to a mounting base and can all be substantially verticallyoriented. The tuning device can be designed to be insertable in and outof the mounting base so as to be positioned at a different height withrespect to the light energy sources. The position of the tuning devicecan be controlled using a controller if desired.

Other objects, features and aspects of the present invention arediscussed in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a cross-sectional view of one embodiment of a thermalprocessing chamber that may be used in accordance with the presentinvention;

FIG. 2 is a plan view of one embodiment of a heating device that may beused in thermal processing chambers made in accordance with the presentinvention;

FIG. 3 is a cross sectional view of one embodiment of a tuning devicefor use in the present invention;

FIG. 4 is a plan view of an alternative embodiment of a heating devicethat may be used in thermal processing chambers in accordance with thepresent invention;

FIG. 5 is a partial perspective view of an alternative embodiment of atuning device made in accordance with the present invention;

FIG. 6 is an enlarged portion of the tuning device shown in FIG. 5illustrating how light energy may be reflected off the surface of thedevice; and

FIG. 7 is a graphical representation of the results obtained in theExample which follows.

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

A rapid thermal processing apparatus uses intense light to heat asemiconductor wafer as part of the manufacturing process of integratedcircuits. Exposure to light energy, which is also referred to herein aslight energy, causes a rapid increase in the temperature of asemiconductor wafer and allows processing times to be relatively short.In rapid thermal processing systems, it is important to radiate thewafer with very high intensity light in a very uniform and controlledfashion. As stated above, the difficulty with current devices is thatthe requirements for the intensity of the radiated light and the abilityto heat wafers uniformly are very difficult to achieve.

In general, the present invention is directed to an apparatus and methodfor heating semiconductor wafers uniformly and at a controlled rate. Theapparatus includes a thermal processing chamber in communication with aheating device that is used to heat treat semiconductor wafers containedin the chamber. The heating device contains a plurality of lamps thatare positioned at preselected locations for heating the wafers. Inparticular, the lamps emit light energy and form a irradiancedistribution over the surface of the wafer.

During heating, the wafer is rotated with respect to the plurality oflamps. In this manner, the lamps form radial heating zones on the wafer.The energy supplied to each heating zone can be controlled while thewafer is being heated.

In one embodiment, the temperature at different locations of the waferis monitored. Based upon the temperature sensed at the differentlocations, the energy being emitted by the lamps is selectivelycontrolled.

In accordance with the present invention, the heating device incommunication with the thermal processing chamber further containstuning devices which are designed to modify the irradiance distributionof the heating lamps for more uniformly heating the semiconductor wafer.The tuning devices allow fine adjustments to be made to the waferirradiance distribution pattern in order to heat the wafer under a morecontrolled temperature regime and more uniformly. The tuning device canbe, in one embodiment, a localized and focused source of light energythat can be directed onto a particular location on the wafer. In analternative embodiment, however, the tuning device can be a passivedevice which redirects light energy being emitted by the heating lampsin a manner that heats the wafer more uniformly.

For instance, the tunning device can be an active localized source suchas a tungsten halogen bulb in an optical configuration or a laser diodewith relatively high power. Alternatively, the tuning device can be apassive device that is used to distort and optimize the radiation of thelight energy sources and create a desired uniform illumination.

Referring to FIG. 1, a system generally 10 made in accordance with thepresent invention for heat treating a wafer made from a semiconductivematerial, such as silicon, is illustrated. System 10 includes aprocessing chamber 12 adapted to receive substrates such as a wafer 14for conducting various processes. As shown, wafer 14 is positioned on asubstrate holder 15 made from a thermal insulating material such asquartz. Chamber 12 is designed to heat wafer 14 at very rapid rates andunder carefully controlled conditions. Chamber 12 can be made fromvarious materials, including metals and ceramics. For instance, chamber12 can be made from stainless steel or quartz.

When chamber 12 is made from a heat conductive material, preferably thechamber includes a cooling system. For instance, as shown in FIG. 1,chamber 12 includes a cooling conduit 16 wrapped around the perimeter ofthe chamber. Conduit 16 is adapted to circulate a cooling fluid, such aswater, which is used to maintain the walls of chamber 12 at a constanttemperature.

Chamber 12 can also include a gas inlet 18 and a gas outlet 20 forintroducing a gas into the chamber and/or for maintaining the chamberwithin a preset pressure range. For instance, a gas can be introducedinto chamber 12 through gas inlet 18 for reaction with wafer 14. Onceprocessed, the gas can then be evacuated from the chamber using gasoutlet 20.

Alternatively, an inert gas can be fed to chamber 12 through gas inlet18 for preventing any unwanted or undesirable side reactions fromoccurring within the chamber. In a further embodiment, gas inlet 18 andgas outlet 20 can be used to pressurize chamber 12. A vacuum can also becreated in chamber 12 when desired, using gas outlet 20 or an additionallarger outlet positioned beneath the level of the wafer.

During processing, substrate holder 15, in one embodiment, can beadapted to rotate wafer 14 using a wafer rotation mechanism 21. Rotatingthe wafer promotes greater temperature uniformity over the surface ofthe wafer and promotes enhanced contact between wafer 14 and any gasesintroduced into the chamber. It should be understood, however, thatbesides wafers, chamber 12 is also adapted to process optical parts,films, fibers, ribbons, and other substrates having any particularshape.

A heat source or heating device generally 22 is included incommunication with chamber 12 for heating wafer 14 during processing.Heating device 22 includes a plurality of lamps 24, such astungsten-halogen lamps. As shown in FIG. 1, lamps 24 are placed abovewafer 14. It should be understood, however, that lamps 24 may be placedat any particular location. Further, additional lamps could be includedwithin system 10 if desired.

The use of lamps 24 as a heat source is generally preferred. Forinstance, lamps have much higher heating and cooling rates than otherheating devices, such as electrical elements or conventional furnaces.Lamps 24 create a rapid isothermal processing system that provideinstantaneous energy, typically requiring a very short and wellcontrolled start up period. The flow of energy from lamps 24 can also beabruptly stopped at any time. As shown in the figure, lamps 24 areequipped with a gradual power controller 25 that can be used to increaseor decrease the light energy being emitted by any of the lamps.

In order to assist in directing the light energy being emitted by lamps24 onto wafer 14, the lamps can be associated with a reflector or a setof reflectors. For instance, mounting base 34 can include a reflectivesurface that surrounds the lamps. In one embodiment, reflective angularrecesses can be formed into a mounting base 34 for directing the lightenergy onto the wafer.

Referring to FIG. 2, in one alternative embodiment, heating device 22can include arc-shaped reflector plates 36 which are located in betweenthe concentric rings of lamps 24. Reflector plates 36 are substantiallyvertically oriented with respect to a wafer placed in communication withheating device 22 and extend at least a portion of the length of lamps24. More particularly, arc-shaped reflector plates 36 can extend lessthan the length of lamps 24 about the same length as lamps 24 or beyondthe length of lamps 24. Reflector plates 36 serve to direct the lightenergy being emitted by the concentric rings of lamps. Besidesarc-shaped reflector plates 36, however, it should be understood thatvarious other reflective devices may be used in heating device 22.

In order to monitor the temperature of wafer 14 during the heatingprocess, in this embodiment, thermal processing chamber 12 includesplurality of radiation sensing devices generally 27. Radiation sensingdevices 27 include a plurality of optical fibers or light pipes 28 whichare, in turn, in communication with a plurality of corresponding lightdetectors 30. Optical fibers 28 are configured to receive thermal energybeing emitted by wafer 14 at a particular wavelength. The amount ofsensed radiation is then communicated to light detectors 30 whichgenerate a usable voltage signal for determining the temperature of thewafer which can be calculated based, in part, on Planck's Law. In oneembodiment, each optical fiber 28 in combination with a light detector30 comprises a pyrometer. In another embodiment, the optical fibers 28are routed to a single but multiplexing radiation sensing device.

In general, thermal processing chamber 12 can contain one or a pluralityof radiation sensing devices. In a preferred embodiment, as shown inFIG. 1, thermal processing chamber 12 contains a plurality of radiationsensing devices that measure the temperature of the wafer at differentlocations. Knowing the temperature of the wafer at different locationscan then be used to control the amount of heat being applied to thewafer as will be described in more detail hereinafter. The amount ofheat applied to various zones of the wafer can also be controlled in anopen loop fashion. In this configuration the ratios between the variousheating zones can be pre-determined after manual optimization. Insubsequent processes, these ratios are used with no changes during theheating cycles.

During the process of the present invention, system 10 should bedesigned such that optical fibers 28 only detect thermal radiation beingemitted by wafer 14 and not detect radiation being emitted by lamps 24.In this regard, system 10 includes a filter 32 which prevents thermalradiation being emitted by lamps 24 at the wavelength at which lightdetectors 30 operate from entering chamber 12. Filter 32 also serves toisolate lamps 24 from wafer 14 and prevent contamination of the chamber.Filter 32 as shown in FIG. 1 can be a window positioned between chamber12 and heat source 22. In an alternative embodiment, each lamp 24 can becovered by a separate filter.

In one embodiment, filter 32 is made from fused silica or quartz. Fusedsilica is known to absorb thermal radiation very effectively at selectedwavelengths. For instance, synthetic fused silica with highconcentration of OH ions is very effective at absorbing light at awavelength of from approximately 2.7 micrometers to about 2.8micrometers. Thus, in one embodiment, when filter 32 is made fromsynthetic fused silica, light detectors 30 can be configured to detectthermal radiation being emitted by wafer 14 at a wavelength of about 2.7micrometers. In other embodiments, the separation between radiationarriving to the sensor from the wafer and lamps is achieved bymechanical means of isolation. In these embodiments, buffers and shieldsare present to prevent a direct path from forming between a light sourceand a sensing port.

Besides using radiation sensing devices, other temperature sensingdevices may be used in the system of the present invention. Forinstance, one or more thermocouples may be incorporated into the systemfor monitoring the temperature of the wafer at a single location or at aplurality of locations. The thermocouples can be placed in directcontact with the wafer or can be placed adjacent the wafer from whichthe temperature can be extrapolated.

System 10 further includes a system controller 50 which can be, forinstance, a microprocessor. Controller 50 receives voltage signals fromlight detectors 30 that represent the radiation amounts being sampled atthe various locations. Based on the signals received, controller 50 isconfigured to calculate the temperature of wafer 14 at differentlocations.

System controller 50 as shown in FIG. 1 can also be in communicationwith lamp power controller 25. In this arrangement, controller 50 candetermine the temperature of wafer 14, and, based on this information,control the amount of thermal energy being emitted by lamps 24. In thismanner, instantaneous adjustments can be made regarding the conditionswithin reactor 12 for processing wafer 14 within carefully controlledlimits.

In one embodiment, controller 50 can also be used to automaticallycontrol other elements within the system. For instance, controller 50can be used to control the flow rate of gases entering chamber 12through gas inlet 18. As shown, controller 50 can further be used tocontrol the rate at which wafer 14 is rotated within the chamber.

As described above, the present invention is generally directed to aparticular heating configuration that is used within thermal processingchamber 12. Referring to FIG. 2, one embodiment of a heating device 22that can be used in combination with thermal processing chamber 12 inaccordance with the present invention is illustrated. As shown, heatingdevice 22 includes a plurality of light energy sources, such as lamps 24that are secured to a mounting base 34. In this embodiment, lamps 24 arearranged in five concentric rings which each serve to heat a separateradial zone on a wafer. It should be understood, however, that manyother lamp configurations may be used without limitation.

In accordance with the present invention, in order to heat a wafer moreuniformly, heating device 22 further includes tuning devices 40 which,in this embodiment, are generally positioned in between the concentricrings of lamps 24. Tuning devices 40 are designed to emit controlled andfocused amounts of light energy onto particular locations of asemiconductor wafer being heated. The tuning devices are provided inorder to make fine adjustments to the irradiance distribution producedby lamps 24 in order to more precisely heat the wafers. For example,tuning devices 40 can be used to emit controlled amounts of light energybetween the radial heating zones located on the wafer.

Tuning devices 40 as shown in FIG. 2 are active localized sources offocused light energy. The tuning devices can be, for instance, laserdiodes having a relatively high power. In an alternative embodiment, asshown in FIG. 3, tuning devices 40 can be a lamp, such as a tungstenhalogen lamp, in operative association with one or more focusing lenses.

As shown particularly in FIG. 3, tuning device 40 includes a lightenergy source 42 that is spaced a predetermined distance from a firstfocusing lens 44 and a second focusing lens 46. Focusing lenses 44 and46 are designed to focus a beam of light energy being emitted by lightenergy source 42 onto a desired location of a semiconductor wafer 14. Inthis embodiment, tuning device 40 is recessed in relation to lamps 24shown in FIG. 2. Thus, as shown, tuning device 40 is placed behind anopening formed into a wall 48 of heating device 22. Wall 48 as shown inFIG. 2 is located behind lamps 24. It should be understood, however,that tuning device 40 can also be placed on the other side of wall 48 inthe same plane as lamps 24.

As shown in FIG. 3, light energy source 42 and focusing lenses 44 and 46can be mounted to a support structure 60. Support structure 60 caninclude a tiltable lever arm which allows for an adjustment to be madein the position of the tuning device. In particular, support structure60 can be tilted for focusing light energy being emitted by the lightenergy source onto desired locations of wafer 14.

During operation, heating device 22 is preferably in communication witha system controller 50 as shown in FIG. 1. Based upon the temperature ofthe wafer being heated, system controller 50 can be designed to vary theamount of light energy being emitted by lamps 24 and by tuning devices40. Each of the lamps that make up a concentric ring can be controlledtogether in order to form radial heating zones on the wafer. Tuningdevices 40 on the other hand, can be controlled by system controller 50independent of the concentric rings in a manner that enhancestemperature uniformity throughout the wafer. System controller 50 canalso be used to control support structure 60 for automatically directinglight energy being emitted by tuning device 40 onto a desired locationof the wafer.

As described above, besides using localized active sources, the tuningdevices of the present invention can also comprise passive sources whichare used to adjust and vary the irradiance distribution of the heatinglamps in a manner that enhances wafer temperature uniformity. Oneembodiment of a system using passive tuning devices is illustrated inFIG. 4. As shown, a heating device generally 122 for use in thermalprocessing chamber 12 as shown in FIG. 1 is illustrated. Heating device122 includes an assembly of lamps 124 secured to a mounting base 134,which includes a base plate 148. In this embodiment, lamps 124 arespaced at various locations on mounting base 134 and are designed toform many different radial heating zones on a wafer.

In accordance with the present invention, heating device 122 furtherincludes tuning devices 140 which are positioned adjacent to selectedlamps. In this embodiment, tuning devices 140 are optical elementsdesigned to redirect a portion of the radiant energy being emitted bythe lamp assembly, thereby allowing fine adjustments to the irradiancedistribution of the heater device onto a wafer located below theassembly.

In this particular embodiment, the optical elements are rectangularshaped and are inserted into heating device 122 generally near one ormore of the lamps 124. Heater device 122 can be designed such that thedepth of insertion of tuning devices 140 and the azimuthal angle of thetuning devices can be adjusted. For instance, tuning devices 140 can beinserted through an opening formed into base plate 148 and can beextended into the heater device any desired length in relation to thelength of lamps 124. Similarly, in some systems, the angle at which thetuning devices are inserted can be adjusted.

The purpose of tuning devices 140 is to cause the radiation beingemitted from lamps 124 to deviate from an original azimuthal directionof propagation in order to modify the radial power distribution on thewafer. Desirably, the light energy being emitted by the lamps exitsheater device 122 sooner than it would otherwise without tuning devices140 and will hit and contact the wafer at a different radial locationthan it would otherwise. By selectively varying the location of tuningdevices 140, the wafer can be heated under a more controlled and uniformtemperature regime.

In order to redirect the light energy that is being emitted by lamps124, tuning devices 140 include at least one surface having desiredoptical characteristics. In modifying the irradiance distribution of thelamps, tuning devices 140 can either reflect light energy, refract lightenergy, or can even absorb light energy.

One preferred embodiment of a tuning device 140 that can be used toreflect light energy in a desired manner is illustrated in FIG. 5. Asshown, tuning device 140 includes a ruled prismatic surface 162. Asshown, surface 162 is serrated and mirrored. The prismatic surfaceillustrated in FIG. 5 employs a fixed pitch with a fixed facet angle. Itshould be understood, however, that the surface could also employ afixed pitch with a variable facet angle.

By including a ruled prismatic surface, tuning device 140 causes radiantenergy contacting the device to exit heater device 122 sooner than wouldotherwise occur. This device alters the radial irradiance distributionof the system in a way that can be finely adjusted over somepreestablished range.

Referring to FIG. 6, a simplified detail of light energy reflecting offof one facet of tuning device 140 is illustrated. As shown, horizontalrays incoming from the left of surface 162 contact the tuning device andexit with a dramatically different vertical orientation. As describedabove, besides using a fixed facet angle, tuning device 140 can also bemade with a variable angle design. When using a variable angle design,tuning device 140 can be used to more accurately focus light radiationcontacting surface 162 and more accurately redirect the light energyonto a particular location on the wafer being heated if desired.

It should be understood, however, that numerous other surface structuresare possible. For instance, in an alternative design, surface 162 oftuning device 140 can be planar and diffusing, causing light energycontacting the surface to scatter in all directions. For instance, ahighly diffuse surface may be a rough but highly reflective surface ontuning device 140. Using a diffuse surface may be less costly to producebut may not provide a similar amount of control as using a prismaticsurface.

As stated above, tuning device 140 can be designed to either reflectlight radiation, refract light radiation or absorb light radiation. Whenused to reflect light radiation, preferably tuning device 140 is coatedwith a highly reflective material, such as a dielectric material or apolished metal, such as gold, copper, or aluminum. When used to refractor absorb light energy, tuning device 140 can be made, for instance,from quartz.

The present invention may be better understood with reference to thefollowing example.

EXAMPLE

The following example was conducted in order to demonstrate how a tuningdevice made in accordance with the present invention can be used tochange the irradiance distribution of light energy sources.

A prismatic tuning device similar to the one illustrated in FIG. 5 wasinserted into an array of light energy sources in a thermal processingchamber. The array of light energy sources included five concentricrings of vertically orientated lamps mounted to a base, similar to theheating device illustrated in FIG. 4. The prismatic tuning device waspositioned adjacent one of the lamps located on the second concentricring from the center of the array of lamps.

Specifically, in this example, only the second concentric ring of lampswas turned on in order to measure its effect. Light intensity was thenmeasured at different radial locations at the same distance from thelight source as the semiconductor wafer would be placed. In particular,light intensity was measured when the tuning device was positionedadjacent to one of the light energy sources and when the tuning devicewas absent from the heating device. The results of the example areillustrated in FIG. 7. Also illustrated in the Figure is a graph of thedifference in relative intensity between when the prismatic element wasinserted and when it was not. (The scale for the difference is on the Yaxis on the right.)

As shown by the figure, inclusion of the tuning device of the presentinvention changed the irradiance distribution of the light energysources of particular advantage, the tuning device only slightlymodified the irradiance distribution. In this manner, the tuning deviceof the present invention is well suited to making fine adjustments inthe manner in which a wafer is illuminated in order to promotetemperature uniformity.

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention, which ismore particularly set forth in the appended claims. In addition, itshould be understood that aspects of the various embodiments may beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the invention sofurther described in such appended claims.

What is claimed is:
 1. An apparatus for heat treating semiconductorwafers comprising: a thermal processing chamber adapted to contain asemiconductor wafer; and a heating device in communication with saidthermal processing chamber for heating a semiconductor wafer in saidchamber, said heating device comprising: (a) a plurality of light energysources configured to emit light energy onto said semiconductor wafer,said light energy sources being positioned so as to form an irradiancedistribution across a surface of said semiconductor wafer; and (b) atleast one tuning device positioned amongst said light energy sources,said tuning device being configured to emit focused amounts of lightenergy, said tuning device comprising a light energy source spaced fromat least one optical element comprising at least one focusing lens, saidoptical element being configured to focus and direct light energy beingemitted by said light energy source onto said semiconductor wafer at aparticular location in a manner for more uniformly heating saidsemiconductor wafer.
 2. An apparatus as defined in claim 1, furthercomprising a substrate holder for holding said semiconductor wafer, saidsubstrate holder being configured to rotate said wafer.
 3. An apparatusas defined in claim 1, wherein said tuning device is mounted in amovable support structure.
 4. An apparatus as defined in claim 3,wherein said support structure comprises a tiltable lever arm.
 5. Anapparatus as defined in claim 1, wherein said light energy source andsaid at least one focusing lens are mounted on a support structure, saidsupport structure being movable for directing light energy emitted fromsaid light energy source onto a determined location on saidsemiconductor wafer.
 6. An apparatus as defined in claim 5, wherein thesaid support structure comprises a tiltable lever arm.
 7. An apparatusas defined in claim 1, further comprising: at least one temperaturesensing device for sensing the temperature of said semiconductor waferat least one location; and a controller in communication with said atleast one temperature sensing device and at least one of said lightenergy sources, said controller being configured to control the amountof light energy being emitted by said light energy sources in responseto temperature information received from said at least one temperaturesensing device.
 8. An apparatus as defined in claim 7, wherein saidcontroller is configured to control the amount of light energy beingemitted by said tuning device independently of said plurality of lightenergy sources.
 9. An apparatus as defined in claim 1, wherein saidapparatus contains at least three of said tuning devices.
 10. Anapparatus as defined in claim 1, wherein said plurality of light energysources are horizontally oriented with respect to said semiconductorwafer.
 11. An apparatus for heat treating semiconductor waferscomprising: a thermal processing chamber adapted to contain asemiconductor wafer; and a heating device in communication with saidthermal processing chamber for heating a semiconductor wafer in saidchamber, said heating device comprising: (a) a plurality of light energysources configured to emit light energy into said semiconductor wafer,said light energy sources being positioned so as to form an irradiancedistribution across a surface of said wafer; and (b) at least one tuningdevice comprising a laser diode, said laser diode emitting light energyonto a determined location on said semiconductor wafer in order to moreuniformly heat said semiconductor wafer.
 12. An apparatus as defined inclaim 11, further comprising a substrate holder for holding saidsemiconductor wafer, said substrate holder being configured to rotatesaid wafer.
 13. An apparatus as defined in claim 11, wherein said tuningdevice is mounted in a movable support structure.
 14. An apparatus asdefined in claim 11, wherein said tuning device is adjustable fordirecting light energy being emitted from said at least one laser diodeonto a determined location on said semiconductor wafer in order to moreuniformly heat said semiconductor wafer.
 15. An apparatus as defined inclaim 11, further comprising: at least one temperature sensing devicefor sensing the temperature of said semiconductor wafer at least onelocation; and a controller in communication with said temperaturesensing device with at least certain of said light energy sources, andwith said tuning device, said controller being configured to control theamount of light energy being emitted by said light energy sources andsaid tuning device in response to temperature information received fromsaid temperature sensing device.
 16. An apparatus as defined in claim15, wherein said controller is configured to control the amount of lightenergy being emitted by said at least one tuning device independently ofsaid light energy sources.
 17. An apparatus as defined in claim 11,wherein said apparatus contains at least three of said tuning devices.18. An apparatus as defined in claim 11, wherein said plurality of lightenergy sources are horizontally oriented with respect to saidsemiconductor wafer.
 19. An apparatus for heat treating semiconductorwafers comprising: a thermal processing chamber adapted to contain asemiconductor wafer; and a heating device in communication with saidthermal processing chamber for heating a semiconductor wafer containedin said chamber, said heating device comprising: (a) a plurality oflight energy sources configured to emit light energy onto saidsemiconductor wafer, said light energy sources being positioned so as toform an irradiance distribution across a surface of said wafer, thelight energy sources being horizontally oriented with respect to thesemiconductor wafer, each of said light energy sources comprising afirst lamp device; and (b) at least one tuning device positioned amongstsaid light energy sources, said tuning device being generally verticallyoriented with respect to the semiconductor wafer and comprising a secondlamp device, wherein said first lamp device is different from saidsecond lamp device, the tuning device emitting localized and focusedlight energy in a manner for more uniformly heating the semiconductorwafer.
 20. An apparatus as defined in claim 19, further comprising asubstrate holder for holding said semiconductor wafer, said substrateholder being configured to rotate said wafer.
 21. An apparatus asdefined in claim 19, wherein said tuning device is mounted in a movablesupport structure.
 22. An apparatus as defined in claim 19, furthercomprising: at least one temperature sensing device for sensing thetemperature of said semiconductor wafer at least one location; and acontroller in communication with said temperature sensing device with atleast certain of said light energy sources, and with said tuning device,said controller being configured to control the amount of light energybeing emitted by said light energy sources and said tuning device inresponse to temperature information received from said temperaturesensing device.
 23. An apparatus as defined in claim 22, wherein saidcontroller is configured to control the amount of light energy beingemitted by said at least one tuning device independently of said lightenergy sources.
 24. An apparatus as defined in claim 19, wherein saidapparatus contains at least three of said tuning devices.
 25. Anapparatus as defined in claim 19, wherein said tuning device comprises alaser diode.
 26. An apparatus as defined in claim 25, wherein saidplurality of light energy sources comprises tungsten halogen lamps. 27.An apparatus for heat treating semiconductor wafers comprising: athermal processing chamber adapted to contain a semiconductor wafer; anda heating device in communication with said thermal processing chamberfor heating a semiconductor wafer in said chamber, said heating devicecomprising: (a) a plurality of light energy sources configured to emitlight energy onto said semiconductor wafer, said light energy sourcesbeing positioned so as to form an irradiance distribution across asurface of said semiconductor wafer; and (b) at least one tuning devicecomprising a prismatic surface, said tuning device positioned amongstsaid light energy sources, said tuning device being configured to directlight energy being emitted by said light energy sources onto saidsemiconductor wafer in a manner for more uniformly heating saidsemiconductor wafer.
 28. An apparatus as defined in claim 27, furthercomprising a substrate holder for holding said semiconductor wafer, saidsubstrate holder being configured to rotate said wafer.
 29. An apparatusas defined in claim 27, wherein said tuning device is mounted in amovable support structure.
 30. An apparatus as defined in claim 29,wherein said support structure comprises a tiltable lever arm.
 31. Anapparatus as defined in claim 27, wherein said prismatic surface has afixed pitch and a fixed facet angle.
 32. An apparatus as defined inclaim 27, wherein said prismatic surface has a fixed pitch with avariable facet angle.
 33. An apparatus as defined in claim 27, whereinthe height of said optical element is adjustable with respect to saidlight energy sources.
 34. An apparatus as defined in claim 27, whereinsaid apparatus contains at least three of said tuning devices.
 35. Anapparatus as defined in claim 27, further comprising: at least onetemperature sensing device for sensing the temperature of saidsemiconductor wafer at at least one location; and a controller incommunication with said at least one temperature sensing device and atleast one of said light energy sources, said controller being configuredto control the amount of light energy being emitted by said light energysources in response to temperature information received from said atleast one temperature sensing device.
 36. An apparatus as defined inclaim 27, wherein said prismatic surface comprises a ruled prismaticsurface.
 37. An apparatus as defined in claim 27, wherein said tuningdevice reflects light energy being emitted by said light energy sources.38. An apparatus as defined in claim 27, wherein said tuning devicerefracts light energy being emitted by said light energy sources.
 39. Anapparatus as defined in claim 27, wherein said prismatic surface is madefrom a highly reflective material having a reflectivity of at least 0.9at a wavelength being emitted by said light energy sources.
 40. Anapparatus as defined in claim 27, wherein said prismatic surfacecomprises a diffuse surface for reflecting and scattering light energy.